iommu/io-pgtable-arm: Add way to debug pgtable walk

Add an io-pgtable method to walk the pgtable returning the raw PTEs that
would be traversed for a given iova access.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Mostafa Saleh <smostafa@google.com>
Link: https://lore.kernel.org/r/20241210165127.600817-4-robdclark@gmail.com


[will: Removed 'arm_lpae_io_pgtable_walk_data::level' per Mostafa]
Signed-off-by: Will Deacon <will@kernel.org>